(a) Field of the Invention
The present invention relates to a drawn polyethylene terephthalate (PET) fiber, a PET tire cord, their preparation methods, and a tire including the same. More particularly, the present invention relates to a drawn PET fiber that has good dimensional stability, thereby increases the high speed driving performance of a tire, a PET tire cord, their preparation methods, and a tire including the same.
(b) Description of the Related Art
A tire is a complex body of fiber/steel/rubber, and generally has a structure as illustrated in FIG. 1. That is, the steel and fibers cord take a role of reinforcing the rubber and form a basic skeletal structure in the tire. It is, so to speak, like the role of a bone in a human body.
As reinforcement for the tire, the performance factors such as fatigue resistance, shear strength, durability, repelling elasticity, adhesion to a rubber, and the like are required to the cord. Therefore, various cords made of suitable materials are used according to the performances required to the tire.
Recently, rayon, nylon, polyester, steel, aramid, and the like are generally used as the materials for the cord, and the rayon and the polyester are used for a body ply (or a carcass) (6 in FIG. 1), the nylon is mainly used for a cap ply (4 in FIG. 1), and the steel and the aramid are mainly used for a tire-belt part (5 in FIG. 1).
The structure and the characteristics of the tire represented in FIG. 1 are briefly disclosed hereinafter.
Tread 1: A part contacting the road surface; this part must provide a friction force necessary for braking and driving, be good in abrasion resistance, and also be able to stand up against an external shock, and its heat generation must be small.
Body ply (or Carcass) 6: A cord layer inside the tire; this part must support a load and stand against a shock, and its fatigue resistance against bending and stretching movement during driving must be good.
Belt 5: This part is located between the body plies and is mostly composed of steel wire, and it lessens the external shock and also makes the ground contacting surface of the tread wide and the driving stability good.
Side wall 3: A rubber layer between the lower part of the shoulder 2 and the bead 9; it takes a role of protecting the internal body ply 6.
Bead 9: A square or hexagonal wire bundle, wherein a rubber is coated on the steel wires; it takes a role of fitting and fixing the tire to a rim.
Inner liner 7: A part located inside the tire instead of a tube; it makes a pneumatic tire possible by preventing air leakage.
Cap ply 4: A special cord fabric located on the belt of a radial tire for some passenger cars; it minimizes the movement of the belt during driving.
Apex 8: A triangular rubber packing material used for minimizing the dispersion of the bead, protecting the bead by relieving external shock, and preventing an air inflow during shaping.
Recently, developments for tires suitable for high speed driving are required as the passenger cars are gentrified, and accordingly the stability during high speed driving and high durability of the tire are recognized as very important characteristics. Furthermore, the performance of the materials for the cap ply cord importantly comes to the force before everything else for satisfying the characteristics.
The steel belt inside the tire is generally arranged in the oblique direction, however the steel belt tends to move toward the circumferential direction during high speed driving, and there are some problems that the sharp ends of the steel belt may cause separation between the layers of the belt and shape deformation of the tire by cutting the rubber or generating cracks. The cap ply prevents the separation between the layers and deformation of the shape of the tire and takes a role of improving the high speed durability and the driving stability by restraining the movement of the steel belt.
A nylon 66 cord is mainly used for a general cap ply cord. The nylon 66 cord may show the effect of restraining the movement of the belt by exhibiting high shrinkage force at the stiffening temperature of 180□ and wrapping the steel belt, however, it has disadvantages in that partial deformation may be caused by the load of the tire and the car and it may clatter during driving because it has low dimensional stability.
Furthermore, the shape of the nylon 66 cord may be easily deformed and the deformed nylon 66 results in tire deformation when the load given to the nylon 66 cord is changed by a change of the driving speed of the car and the controllability and the riding comport of a car may be decreased accordingly, because the nylon 66 cord has low dimensional (shape) stability.
On the other hand, a general PET fiber or a PET high modulus low shrinkage (HMLS) fiber that is mostly used as an industrial fiber has good dimensional stability in comparison with the nylon 66, but the external shape of the cord composed of the fibers may be easily deformed and may deform the tire when the driving speed of the car is suddenly increased, because the general PET fiber or the PET HMLS fiber does not have sufficient dimensional stability either. Therefore, even in case of using the cord composed of the fibers as the cap ply cord, the high speed driving performance of the tire, the controllability or the riding comport of the car are insufficient.